It is well established that numerous cellular activities are regulated by the concentration of intracellular calcium which is in turn regulated by the sarcoplasmic reticulum. The overall goal of this research proposal is to understand the basic mechanisms by which the SP regulates cardiac and skeletal muscle contraction. This will be achieved by studying the transient-state kenetics of the Ca2 ion-Mg2 ion-ATPase of the SR using a rapid mixing quench-flow apparatus. The time course of three experimentally measurable parameters will be studied in the millisecond (0-200) time range. These parameters are the formation and decomposition of the acid stable phosphorylated intermediate of the Ca2 ion-Mg2 ion-ATPase, the liberation of inorganic phosphate and Ca2 ion transport into the lumen of the Sr vesicle. The experimental data will be used to test and refine models of the SR reaction mechanism; to identify reaction intermediates; and to obtain values for the rate constants of the individual steps in the reaction mechanism. Both analog and digital computer programs will be used for the analysis of the data. In a variety of disease states in both animal and human heart, studies of calcium binding, uptake and release by isolated SR preparation have indicated an involvement of the organelle in myocardial pathology. Similarly, it has been shown that SR isolated from dystrophic muscle is damaged. The proposed studies characterizing the reaction mechanism of normal SR will provide a more firm basis for understanding SP defects that are known to occur in a variety of disease states.